Biochemist Shane Charter is alleged to have provided Stephen Dank - a central figure in the scandal - with supplements sourced from Asia.

It is understood Mr Dank worked closely with Mr Charter to provide players with supplements, which are believed to have cost as much as $30,000. Mr Dank is believed to have been sacked after the club discovered unauthorised expenditure.

Mr Charter, a former champion weightlifter, has advised some of the AFL's best players and other sports stars on nutrition and supplements to boost performance.

He was arrested by Victorian drug squad detectives in 2004 and found to be in possession of 100,000 pseudoephedrine-based tablets - a precursor chemical used to make speed - in bottles labelled vitamin B supplements. He pleaded guilty and received a reduced prison sentence after striking a deal with Crown prosecutors to give evidence against his co-accused, who was later cleared.

Mr Charter declined to comment on Wednesday. However, a supporter of Mr Charter's confirmed his association with Essendon and said he had provided the club with ''vitamins''.

The supporter also said Mr Charter had written to the Therapeutic Goods Administration last year seeking clarification on certain types of peptides.

But another source on Wednesday said Mr Charter, who is the director of a company called Dr Ageless Pty Ltd, had imported from China peptides that were on Australia's prohibited import list.

Sources in the supplement and bodybuilding industry said it was well known that Mr Charter operated on the cusp of the law and promoted the use of peptides to some of his clients.

Australian health authorities are understood to have scrutinised Mr Charter and his associates over their importation of certain products.

Mr Charter works as a consultant at the Ageing Australia clinic in Melbourne and is described on the company's website as the ''originator'' of its business model.

Ageing Australia's website promotes the use of testosterone and human growth hormone. The website features a photograph of a model injecting a needle into her stomach.

The clinic's owner, Laurie Williams, said on Wednesday night that his clinic had nothing to do with Essendon and that Mr Charter ''would be sacked before morning''.

Mr Charter is believed to have established contact with Essendon through his relationship with Mr Dank and former AFL players.

Mr Charter previously advised top sportsmen on their fitness, including Olympic swimmer Scott Miller and Brownlow Medal winners Shane Woewodin and Ben Cousins. Fairfax Media is not suggesting any of his former clients ever acted improperly.

A source aware of Mr Charter and Mr Dank's activities with Essendon said ''Steve Dank made them [supplements] and Charter was importing them''. Mr Dank has not returned calls or texts from Fairfax Media.

Essendon's suspended fitness boss, Dean Robinson, has engaged a lawyer from the AFL Coaches Association to deal with this latest controversy, having sought legal advice last year when he was on the verge of being sacked by the Bombers. Robinson has refused to comment.

Dr Robin Willcourt, who runs the Epigenx Integrated Medicine practice at South Yarra's Como Centre, revealed that Mr Dank had met him last year when Mr Dank was ''very concerned'' about the low testosterone and growth hormone levels of his players.

One of the alleged supplements given to players was bovine colostrum. This contains a growth factor called IGF-1 that is on the banned substances list of the International Olympic Committee and the World Anti-Doping Agency.

Senior Essendon players did demand assurances from their coaching and medical staff before being administered the controversial substances.

While it has been confirmed that Essendon medical staff, including veteran club doctor Bruce Reid, raised questions about the controversial supplements, the Essendon players have confirmed they signed consent forms that stated the substance administered was acceptable under the Australian Sports Anti-Doping Code.

The assurances were sought by the leadership group and notably David Hille and skipper Jobe Watson.

A specially convened meeting of Bombers senior-listed players and the AFL Players Association on Wednesday heard that the forms were signed in the presence of Essendon senior coaching staff, doctors and the fitness staff. Coach James Hird, who on Wednesday voiced his support for the suspended Robinson, witnessed the forms being handed out and signed.

The players also signed a separate confidentiality agreement after being told the club did not want its controversial practices being leaked to opposition clubs.

While Hird put his players through their training drills on Wednesday and remained positive, Essendon great Tim Watson said he feared that his son, Jobe, would be stripped of his Brownlow medal should the players be found guilty.

Retired player Mark McVeigh said that he had only been given vitamin B and C injections in a sterile environment, believed to be in a house close to Windy Hill, with a registered nurse present.